N  Profile Rotors

Screw machine manufacturers,
improve the quality of your product with
the world's most advanced profile rotors

Additional N Rotor  Information

Compressor Centre at City University London is entirely involved in design of superior rotor profiles and appropriate screw compressors and this is fully confirmed literally throughout the World. The dry and oil-flooded air compressors as well as refrigeration compressors in various configurations 2/3, 3/5, 4/5, 4/6, 5/6 and 6/7 are created and calculated by use of our design software ‘Scorpath’, which is based on a comprehensive mathematical model of the screw compressor eometry and working process and it is regularly checked by comparison with measured data obtained either on our experimental stands or by our numerous customers. Moreover, the families of our compressors were thoroughly tested by our customers who have published their results. We do not have a single reason to suspect that our further compressor designs would confirm our predictions in full.

Compressor Centre have worked for or with companies in Australia, China, England, Finland, France, Germany, India, Iran, Italy, Korea, Russia, Spain, Turkey and the U.S.A and in former Yugoslavia.

'N' rotor profiles for screw compressors, based on a patented rack  generation procedure, offer greater flow area, less leakage, smaller internal friction and greater lobe strength than any other known rotor profile. More specifically, we can design the rotor profiles within the envelope of your existing compressors, i.e. to retain your previous compressor design and retrofit the rotors only, or to design a new compressor(s) around the 'N' rotors. In both cases a substantial improvement of up to 6.5 % increase in capacity and 2- 2.5 % decrease in specific power will be achieved in comparison with any other rotors of the same size and compressor speed and inlet and outlet pressures.

Using 'Scorpath' software (Screw Compressor Optimal Rotor Profiling And THermodynamics) as a design tool package which calculates and presents screw compressors and their processes and systems, full performance estimates can be carried  out on new designs of these.

Profile Generation

General procedure for screw compressor geometry calculation  is based on a unique rack profile generation. Cross section areas, sealing lines, blow-hole area and screw compressor volume are calculated here. A clearance distribution provides efficient and reliable rotor operation.Tool is  calculated and the unique tool-rotor procedure enables the customer to check the tool profile against any manufacturing errors. For a given built-in volume both, suction and discharge ports are calculated and transferred to a CAD system by the convenient interface.

Patented ‘N’ rotors are calculated by the rack generation procedure. This distinguishes ‘N’ rotors from any other screw compressor rotors. A large blow-hole area, characterizing the rack generated rotors is in ‘N’ rotors overcome by generating the high pressure side of a rack by means of a rotor conjugate action which undercuts a single appropriate curve on the rack. Such rack is then used for profiling both the main and gate rotors.

The following is a brief description of a rack generated "N" rotor profile, typical for a family of rotor profiles designed for the efficient compression of air, common refrigerants and a number of process gases. Rotors are generated by the combined rack-rotor generation procedure. Its features are such that it may be readily modified further to optimize performance for any specific application.

The coordinates of all primary arcs on the rack are summarized here relative to the rack coordinate system. The lobe of the rack is divided into several arcs. The divisions between the profile arcs are denoted by capital letters and each arc is defined separately, as shown in the figure where the rack and rotors are shown.

All curves at ‘N’ profile are given as a "general arc" form of the type: axp+byq=1. Straight lines, circles, parabolae, ellipses and hyperbolae are all easily described by selecting appropriate values for parameters a, b, p and q.

Segment DE is a straight line on the rack, EF is a circular arc of radius r4, segment FG is a straight line for the upper involute, p=q=1, while segment GH on the rack is a meshing curve generated by the circular arc G2H2 on the gate rotor. Segment HJ on the rack is a meshing curve generated by the circular arc H1J1 of the radius r2 on the main rotor. Segment JA is a circular arc of radius r on the rack, AB is an arc which can be either circle, or prabola or hyperbola or ellipse, segment BC is a straight line on the rack matching the involute on the rotor round lobe andnt CD is a circular arc on the rack, radius r3.

If licensed with the 'N' profile rotors, the customer is entitled to the rotor generation procedure which is based on a unique rack profiling method.

Advantages of N rotors compared with others is:

Greater flow area for a given rotor diameter

Smaller leakage area

Stronger female lobes

Involute form of on the rotor contact band

Lower rotor contact forces without risk of rotor 'rattle'

Seizure free rotors


Comparison of N rotors with Sigma, SRM 'D' and Cyclon rotors, less metal - more gas flow

More information.

You can now  download SCORPATH software package to examine N rotors.

Then in your local directory type or press:


This will create \DEMO directory with SCORPATH programs

Then type or press "WMASK" ("MASK" or "HELP") in your \DEMO directory